1. Send him a letter stating that you have not received the keys yet which he claimed as have sent to you informing him that you shall be forced to open the lock by other means in presence of the society secretary if you do not get the keys within next 7 days. Mark a copy of this letter to local police station,
2. After 7 days, get the lock opened by either breaking it or making a duplicate key thereof in presence of the secretary of your society and if there is any item of the leasee still left in the flat, make an inventory thereof taking the signature of the secretary and/or other witnesses and write the leasee to take back his left over items, if any, with in next 7 days otherwise you will not be responsible for its safe keeping. You can also arrange to make a nil inventory to avoid this problem.